Method for producing corrosion-stable and optionally colour/metallically coated and decorative plastic components

ABSTRACT

A method for the manufacture of plastic components that are corrosion-stable, optionally coated in metallic color and decorative first manufactures the components to be coated from a galvanizable plastic in the plastic injection-molding process and then subjects them to a chemical pretreatment, in which a first conductive metal layer is deposited and then an aluminum surface is deposited galvanically. The deposited aluminum surface is oxidized in a subsequent aluminum anodization process.

The invention relates to a method for the manufacture of plastic components that are corrosion-stable, optionally coated in metallic color and decorative, in which the components to be coated are first manufactured from a galvanizable plastic in the plastic injection-molding process and are then subjected to a chemical pretreatment, in which a first conductive metal layer is deposited and then an aluminum is deposited galvanically.

In the automobile industry, diverse and differently decorated plastic components are used for optical enhancement. Conventional surface technologies for such surface-decorated components are the fabrication of undecorated plastic surfaces by injection molding, the lacquering of the plastic surfaces, the graining and etching of the material surfaces to be formed and shaping of these by plastic injection molding, the galvanization of the plastic surface, the decorating in the injection-molding die by IMD (In-Mold Decoration), wherein an imprint printed on a carrier foil is shaped by a carrier foil in the injection-molding process, the back-injection of printed and partly deformed foil inserts stamped in contour-following manner by the FIM technology, the Film-Insert Molding, as well as the back-injection of metal foil.

Besides all of these traditional surface technologies, the imitation of metallic surfaces is trending in the direction of particularly high demand, since this surface gives an impression of high quality and robustness unlike any other.

Besides the components decorated with genuine metal, i.e. blended, joined or back-injected components with thin stainless-steel or aluminum sheets, metallically coated plastic components are also used particularly preferably as decorative elements.

A coating type with which it is possible to achieve optically metallic surfaces is, for example, the gas-phase deposition, to which the PVD method (physical vapor deposition) as well as its modified technologies such as, for example, CVD (chemical vapor deposition) and PeCVD (plasma-enhanced chemical vapor deposition) and others belong. In these processes, thin metal layers are deposited in an evacuated vacuum chamber on a plastic component. The material to be deposited exists in solid form. The vaporized material travels through the coating chamber and impinges on the component to be coated, where layer formation takes place by precipitation. Certainly the PVD method is generally suitable for giving the impression of metallic layers, but it has proved problematic that the very thin metal coating cannot attain sufficient resistance to abrasion and corrosion without an additional protective layer. For this reason, it is necessary to apply a protective layer, for example a clear-lacquer system. In order to achieve adequate basic adhesion to the plastic component to be deposition-coated, a lacquering of a primer is usually also necessary.

A further coating, which is industrially very important, is the galvanic deposition of metals on plastic components. In the process, the parts are first manufactured in the injection-molding process, for example from butadiene-containing copolymers such as ABS or ABS/PC. After the injection-molding process, the components are chemically pretreated, in order that a first thin metal layer, usually a thin nickel or copper layer, can then be deposited on them autocatalytically. In the further galvanic process, further metal layers are then deposited electrolytically, until the galvanization process is finally ended, mostly with a deposited chromium layer.

For all surfaces used, a high force of resistance to mechanical damage as well as also a high resistance to media must exist in addition to the high esthetic demand, in order that subsequent requirements in the automobile exterior as well as in the interior may be met.

Besides all of these requirements to be fulfilled, however, the wish for more individuality, for more design-related freedom and for colored and patterned configuration of the surfaces always also exists. Especially for metallic surfaces such as the galvanic coating, the automobile industry frequently wishes for diversely colored room to choose, but heretofore has been greatly limited in this form of imitation.

The conventional galvanically deposited surface qualities and colors usually range from high gloss through various dullnesses to, by modified electrolytes and processes, to slightly anthracitic and brownish shades.

Surfaces that are optically and haptically metallic as well as colored are usually possible only by laborious additional lacquerings or possibly additional coating on the metal deposit, wherein the adhesion of the lacquer layer or of the coating on the chromium layer must always be regarded as critical and the optical as well as haptic impression of the basic surface is massively restricted. This has its cause in the fact that the deposited chromium layer is very inert and inactive and therefore the (lacquer) layers do not stick.

In order to imitate colored, metallically appearing surfaces, it is also possible, with much effort, for example, to apply a combination of lacquer, gas-phase deposition, for example a PVD coating and a tinted, i.e. weakly pigmented lacquer. Such a technology is described in DE 102 33 120 A1. It is also possible to deposit the metal layers to be deposited directly via special metal alloys in colored manner on the substrate. Such an approach is described in EP 2 369 032 A1. For this purpose, however, a base coat for priming as well as a subsequent coat, namely a clear lacquering is likewise necessary. In this case the color spectrum is greatly limited, however, and the haptic feel is reduced by the lacquer layer.

Here the invention seeks to create a remedy. The task underlying the invention is to create a method for the the manufacture of plastic components that are corrosion-stable, optionally coated in metallic color and decorative, in which it is possible to form a high-quality, corrosion-stable decorative metal layer that also can be optionally colored with a chemical and galvanic pretreatment and at least one galvanic metal deposit.

This task is accomplished by a method having the features of claim 1. Thereafter the deposited aluminum surface is oxidized in a subsequent aluminum anodization process.

With the invention, a method is created for the the manufacture of plastic components that are corrosion-stable, optionally coated in metallic color and decorative, in which it is possible to form a high-quality, corrosion-stable decorative metal layer that also can be optionally colored with a chemical and galvanic pretreatment and at least one galvanic metal deposit.

Preferably the chemical pretreatment is performed by means of selected technologies with mechanical and chemical roughening, swelling and pickling and other technologies for providing an adhesion mechanism for a first conductive metal layer. Hereby the possibility exists of avoiding the traditional pretreatment processes and of using other pretreatment methods. It has also been proved that an adhesion is also obtained by radiation, treatment with swelling and pickling acids beyond chromosulfuric acid (traditional), application of a first conductive layer by PVD or even mixing-in of conductive pigments, in order to form on this the structure and the deposit of a first conductive layer.

In a further development of the invention, the anodized layer is compacted. During compaction, the pores opened by anodization are closed again. Thereby the inclusion of corrosion-promoting substances is prevented.

Other further developments and configurations of the invention are specified in the other dependent claims. An exemplary embodiment of the invention is illustrated in the drawing and will be described in detail in the following, wherein:

FIG. 1 shows the flow diagram of the method according to the invention

For this purpose, the components to be coated are first manufactured in the plastic injection-molding process (a) from a galvanized plastic, preferably from a butadiene-containing copolymer such as ABS or ABS/PC. After the injection-molding process, the components are chemically pretreated in a conventional plastic galvanic process (b), in order that a first thin metal layer, which is usually a thin nickel or copper layer, can be deposited on this machined surface autocatalytically (c). A special form of the catalytic chemical reaction, in which an end product acts as the catalyst for the reaction, is known as autocatalysis (Greek for “self-dissolution”). Due to the progressive formation of this catalysis, the reaction is steadily accelerated.

In the further galvanic process, at least one metal layer is applied galvanically (d) or aluminum is deposited directly in a further galvanic process step (e) and in a subsequent aluminum anodization process is oxidized to an aluminum oxide (f) and may optionally be colored (g).

In accordance with the described process steps, therefore, the method according to the invention is capable of preparing plastic components that are corrosion-stable, optionally coated in metallic color and decorative (h). In the galvanic process step following the chemical pretreatment, an aluminum is deposited, which in the subsequent aluminum anodization process may be oxidized to an aluminum oxide and optionally may be colored.

The aluminum is likewise deposited galvanically from electrolytes or from aluminum salts in organic solutions as well optionally by ionic liquids.

In accordance with the method, therefore, the method according to the invention is able to form, on plastic components, a metallic surface coating that is corrosion-stable, optionally colored and decorative.

The described aluminum anodization process is used just as the already described galvanic process of the plastic galvanization of the electrolysis, wherein oxidation of the aluminum to aluminum (III) oxide is usually performed at the anode using direct current. The transformed aluminum oxide layer is then highly corrosion-resistant and gives a high optical impression.

Prior to the aluminum anodization process, the aluminum-coated components are usually degreased and pickled, in order to remove contamination, deposits and oxide layers that may have been formed. During pickling, existing small surface flaws such as, for example, machining marks, scratches, blowholes, inclusions, etc. are eliminated by material removal.

After anodization, the aluminum-coated component may be dipped in hot dye solution and then rinsed. During coloring with this process, the dye molecules accumulate predominantly in the upper regions of the pores of the anodized aluminum layer and form bonds with the oxide layer.

A coloring of the oxidized aluminum layers may likewise be undertaken using organic dyes. For this purpose, after the anodization, the component is neutralized, rinsed and colored in dye baths containing metal salt solutions. The ions of the solution accumulate in the pores of the anodized aluminum layer and become a solid.

A further possibility for coloring is the electrolytic Colinal process, which is performed with alternating current. The electrolyte contains a color-imparting metal salt. The metal ions penetrate deep into the pores of the layer. The pores filled partly with metal in this way then cause a light-fast coloration due to absorption and scattering effects. Many different color shades are attainable. The duration of the electrolysis depends on the desired color depth.

Particularly appealing optical results are achieved in so-called interference coloring, in which, in contrast to the previous coloring technologies, the color of the aluminum is generated not by included foreign ions but instead by an interference within the aluminum oxide layer. In this situation, light that is reflected at thin layers of optically transparent materials, such as an oil film on water, for example, or as in soap bubbles, frequently appears to be colored. This colored effect is also known as “iridescent colors”, as a consequence of refraction and interference of the light at thin surface layers of an object. Thereby this object appears in the colors of the rainbow. The colors depend on the angle of view. Depending on layer thickness of the oxide layer and on the light extinction associated with it, different colors (e.g. blue, green, gray or red) may be simulated reproducibly.

In order to prevent the inclusion of corrosion-promoting substances, and in order to seal in the color permanently, the pores must be compacted. In a last machining step, the anodized and possibly colored aluminum is compacted in demineralized water by simple cooking. For this purpose it is possible to apply the cooking in hot to boiling water. This may take place by immersion coloring (adsorptive coloring) at temperatures between 55 and 85° C., wherein the process may last between 15 to 30 minutes up to 20 to 35 minutes.

The post-compaction may also take place in post-compaction solution at a temperature between 90 and 100° C. Approximately 3 minutes per 1 μm of layer thickness is needed in this treatment. Alternatively, the treatment may take place in hot water, in which case the water must be de-ionized. The temperature is likewise between 90 and 100° C., wherein a duration of 3 minutes is likewise necessary for 1 μm of layer thickness. 

1. A method for the manufacture of plastic components that are corrosion-stable, optionally coated in metallic color and decorative (h), in which the components to be coated are first manufactured from a galvanizable plastic in the plastic injection-molding process (a) and are then subjected to a chemical pretreatment (b), in which a first conductive metal layer is deposited (c) and then an aluminum surface is deposited galvanically (e), wherein the deposited aluminum surface is oxidized in a subsequent aluminum anodization process (f), wherein the pores of the anodized layer are compacted by boiling in demineralized water.
 2. The method according to claim 1, wherein the chemical pretreatment (b) is carried out according to a conventional plastic galvanization with the following processes: pickling with oxidative metal salt solutions for roughening of the surface, Activation with metal ions, e.g. palladium, as well as autocatalytically proceeding chemical metallization (c) for formation of a first conductive layer of copper, nickel or another metal.
 3. The method according to claim 1, wherein the chemical pretreatment (b) is performed according to selected technologies with mechanical and chemical roughening, swelling and pickling and other technologies for providing an adhesion mechanism for a first conductive metal layer.
 4. The method according to claim 1, wherein, in a subsequent first electrolytic galvanic process (d), at least one metal layer is applied on the pretreated components, on which metal layer aluminum is deposited in a further process step (e).
 5. The method according to claim 4, wherein the aluminum is deposited in a galvanic process step.
 6. The method according to one of the claim 1, wherein aluminum is deposited directly (e) in an electrolytic galvanic process on the components pretreated in such a way.
 7. The method according to claim 1, wherein the deposited aluminum is oxidized to an aluminum oxide in a subsequent aluminum anodization process (f).
 8. The method according to claim 7, wherein the aluminum layer oxidized to an aluminum oxide is colored (g).
 9. (canceled) 